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An intricate geometric form made of clear resin and dried with laser light is in the process of being printed in the Form 2 desktop 3D printer by Formlabs, at CES 2016 in Las Vegas, Nevada, January 7, 2016. (Robyn Beck/AFP/Getty Images)

Engineers at the University of California, San Diego say they have successfully 3D printed life-like liver tissue that simulates how the human liver functions and is structured. The researchers say the tissue could be used as a platform for drug screening.

In the case of Federal Drug Administration (FDA) approval for a drug, on average it takes around 11 to 14 years and $2.6 billion to get a drug to market according to a 2014 study by Tufts University. Around 90% of drugs don't pass animal tests or human clinical trials. In the case of the new 3D printed tissue, the researchers say pharmaceutical companies could use the tissue as platform in the lab to focus on drugs that appear to be more promising and eliminate drugs that have less efficacy.

"The liver plays a critical role in how the body metabolizes drugs and produces key proteins. This is why liver models are increasingly being developed in the lab as platforms for drug screening," said Shu Chien, co-author of the study, professor of Medicine and Bioengineering at UC San Diego and recipient of a National Medal of Science. "However, existing models so far lack both the complex micro-architecture and diverse cell makeup of a real liver."

To create the liver tissue that mimics real human liver tissue, the engineers created a diverse combination of liver cells and supporting cells systematically organized in a hexagonal pattern under a microscope. But to print that complex tissue, they needed a 3D printer that could accommodate the 3D micro-structures found in biological tissue. The team created their own bioprinting tech in the lab capable of reproducing the elements and features of the tissue. The liver tissue was printed in two steps, first by printing a honeycomb pattern of 900-micrometer-sized hexagons and then printing supporting cells into the spaces between the stem-cell-containing hexagons. According to the researchers, the printing process only took a few seconds and was cultured in-vitro for 20 days.

Now, here's why the researchers say this 3D printed tissue has the potential to be a new platform to test the efficacy of a drug. Each of those 3D printed hexagons contained liver cells from human induced pluripotent or embryonic stem cells. Because human stem cells are also patient-specific, researchers don’t need to extract any cells from the liver to build liver tissue in order to build patient-specific drug screening platforms.

After testing, the researchers found their model showed a relatively higher level of a key enzyme considered useful to metabolize drugs administered to patients.